Many proposals have been made and known for a solid catalyst component containing magnesium, titanium, an electron donor compound and halogen as essential components and a process for the polymerization or the co-polymerization of olefins in the presence of a catalyst for polymerization of olefins comprising said solid catalyst component, an organic aluminum compound and an organic silicon compound. For example, JP-A-57-63310 and JP-A-57-63311 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") propose a process for polymerizing an olefin having 3 or more carbon atoms using a catalyst system comprising a solid catalyst component containing a magnesium compound, a titanium compound and an electron donor compound, an organic aluminum compound and an organic silicon compound having Si--O--C bond. However, these processes are not always satisfactory for obtaining highly stereoregular polymers in a high yield, and further improvement has been demanded.
JP-A-63-92614 discloses a solid catalyst component for polymerization of olefins prepared by bringing a dialkoxymagnesium, a diester of an aromatic dicarboxylic acid, an aromatic hydrocarbon, a titanium halide and calcium chloride into contact. On the other hand, JA-A-1-315406 discloses a catalyst system for polymerizing olefins comprising a solid catalyst component prepared by contacting titanium tetrachloride with a suspension formed by diethoxymagnesium with an alkylbenzene, adding phthalic dichloride thereto to react to obtain a solid product, and further contacting the resulting solid product with titanium tetrachloride in the presence of an alkylbenzene, an organic aluminum compound and an organic silicon compound, and a process for polymerizing olefins in the presence of said catalyst system. The foregoing known techniques focus on the development of a catalyst component having a high activity enough to allow the omission of a so-called deashing step, i.e., a step of removing catalyst residues such as chlorine and titanium remaining in the polymer produced as well as on the enhancement of the yield of stereoregular polymer or an improvement in durability of the catalyst activity during polymerization, and achieved excellent results to these purposes.
In the slurry polymerization process which requires a solvent at the polymerization, a polymer having a low molecular weight or a low stereoregularity, which is soluble in a polymerization solvent, is formed, especially in the polymerization of propylene, a polymer so-called "an atactic polypropylene" (hereinafter occasionally referred to as "APP") is formed. In case of increasing of the forming rate of the APP, it concerns about an undesirable effect to the operation of the process and the production cost of a polymer, because a pipeline may be blocked up during polymerization and a step for removal of APP from a high stereoregular polymer to be a product is required after polymerization. Further, in a copolymerization of olefins, for instance, in a random copolymerization of propylene and ethylene, a content of ethylene in a copolymer has to be increased and randomness has to be improved in order to increase the properties of the resulting copolymer. In case that a content of ethylene is increased, the aforementioned problems occur, because the rate for forming a soluble matter on a polymerization solvent tends to be high very much. However, the use of the catalyst of the foregoing known techniques is not enough to solve the problems.
The objective of the present invention is to solve the foregoing problems remaining in the prior art techniques and to provide a solid catalyst component and a catalyst for polymerization of olefins, which can control the rate of forming a polymer having a low molecular weight and a low stereoregular polymer which is soluble in a polymerization solvent and can obtain a high stereoregular polymer in a high yield, and also can obtain a copolymer having excellent properties in a high yield in the copolymerization of olefins.